Of the numerous methods for applying reagents to test strips, in the past electrochemical biosensors have mainly been produced by using printing techniques such as screen printing processes or dispensing techniques for liquid reagent application and subsequent drying, (see. e.g., U.S. Pat. No. 5,437,999 and WO 97/02487). In connection with so-called “capillary fill” test strips, these dispensing methods have successfully been employed, as in the production of Roche Diagnostics AccuChek® Advantage test strips. While these techniques allow for the production of reliable electrochemical biosensors, they are not well suited for high throughput production lines. In addition, these dispensing techniques suffer from the disadvantage of inhomogeneous drying of the reagent, which leads to non-uniform reagent thickness over the covered electrode area. Also, the above mentioned techniques are not suited for the reliable and reproducible production of extremely thin reagent layers (10 μm or less). Therefore, there exists a need for improved reagent application methods.
Blade coating of reagent compositions onto flat substrates has been suggested and successfully been employed in the production of reagent films coated for example on transparent polymeric substrates (e.g., U.S. Pat. Nos. 5,437,999 and 6,036,919). Usually, films of a width of several centimeters to several meters can be produced by this method. For the production of test strips, the so created reagent layers are cut into small stripes and then applied to the test strip substrate. Blade coating of reagent masses has the disadvantage that—although the center portion of the film is homogenous in thickness—at the edge of the coated area inhomogeneities are found which are believed to be due to drying effects and edge effects. While these inhomogeneities are acceptable if broad bands of reagents are coated onto substrates since the inhomogeneous edge portions of the coating can be discarded by edge trim, these inhomogeneities become more and more unacceptable as the reagent stripe to be coated becomes smaller/narrower.
WO 02/057781 discloses a method for manufacturing reagent strips from web material. Among other things, it discloses that the reagent material may be applied to the strip support material by laying down a narrow stripe of reagent material, which may or may not be supported by a support carrier.
U.S. Patent Application Publication 2003/0097981, U.S. Patent Publication Number 2003/0099773, U.S. Pat. Nos. 6,676,995 and 6,689,411 and EP 1 316 367) disclose a solution stripping system for laying down stripes of reagent solutions on a substrate. The system allows slot-die-coating of reagent solutions to web material, e.g., for electrochemical glucose sensors, which solutions have a low viscosity, from about 0.5 to 25 centipoises (cP=mPa−s).
U.S. Pat. Nos. 3,032,008; 3,886,898; and 4,106,437 teach coating apparatuses useful for coating liquid material onto solid supports.
U.S. Pat. No. 6,036,919 discloses reagent films for optical blood glucose test strips. The reagent composition comprises, among other things, a Xanthan gum.
U.S. Patent Application Publication Number 2003/0146113 discloses reagent films for electrochemical coagulation sensors. The reagent composition comprises, among other things, carboxylated microcrystalline cellulose (Avicel® R591) as a film former.
None of the above-mentioned references satisfies the need for a reliable method for forming narrow (for example, less than 1 cm), thin (for example, less than 10 μm) and homogeneous reagent stripes on solid support material for producing test strips, in particular electrochemical test strips.
It is therefore an object of the invention to provide a method and a corresponding reagent composition with which extremely thin, narrow and homogeneous reagent lines or stripes can be deposited onto flat surfaces, for example, of web material and in particular onto the electrode areas of electrochemical biosensor test strips.
This object is reached by the present invention concerning a reagent for a slot-die-coating process for narrow and homogenous reagent stripes.
In a first aspect, the present invention concerns a reagent composition showing shear thinning, slightly thixotropic or thixotropic behavior.
In a second aspect, the present invention concerns a method of coating the shear thinning, slightly thixotropic or thixotropic reagent composition onto web material using a slot-die-coating process.
In a further aspect, the present invention concerns analytical test elements comprising the shear thinning, slightly thixotropic or thixotropic reagent.
In still another aspect, the present invention concerns reagent compositions that are shear thinning and at least slightly thixotropic. It also concerns analytic test elements and methods for making analytic test elements that include using shear thinning and at least slightly thixotropic reagent compositions.